The present invention relates to a series-type hybrid electric vehicle (SHEV) and in particular, to an auxiliary power control system for an SHEV.
A conventional SHEV includes an internal combustion engine (ICE) and an induction motor (IM) that is driven by the engine to generate AC power, which is stored in a battery array (after being converted to DC power). An auxiliary power unit (APU) manages vehicle driving power, as well as charging and discharging of the battery array at predetermined levels.
The auxiliary power unit generates a throttle control signal and a torque control signal in response to a power control signal (based on the driver""s intentions) and a state of charge (SOC) signal from the battery management system (BMS). The auxiliary power unit transmits the throttle control signal to an engine control unit (ECU), and the torque control signal to a generator control unit (GCU). In the GCU, the torque control signal is decoupled into a torque current control signal and a flex current control signal, which are input to different controllers and, ultimately, to a pulse width modulation (PWM) generator and a GCU inverter.
The conventional APU control system is a multi-input multi-output (MIMO) control system generating at least two outputs, i.e., the throttle control signal and the torque control signal, and using two inputs, i.e., the power control signal and the SOC signal. The torque control signal requires additional decoupling and processing. Also, using these two type of output signals creates reliability issues, and requires the auxiliary power unit to process each unique output pair using an additional algorithm.
Additionally, because the internal combustion engine (ICE) and the induction motor (IM) must be simultaneously controlled, and because they have different operational characteristics, real-time control of the ICE and IM using these output control signals is very complex, and must often be conducted by trial-and-error.
Therefore, it would be useful to have an auxiliary power unit that can algorithmically determine a throttle control signal and a voltage control signal, whereby the voltage signal can control the speed of the DC generator directly.
In a preferred embodiment of the present invention, the auxiliary power control system for a series-type hybrid electric vehicle (SHEV) includes a DC generator, a DC/DC converter, a generator control unit, an engine control unit, and an auxiliary power unit controller. The DC generator is driven by an engine for generating DC power. The DC/DC converter converts the DC power generated by the DC generator to a voltage level. The generator control unit controls the voltage level of the DC generator. The engine control unit controls the engine. The auxiliary power unit controller outputs a voltage control signal to the generator control unit, and a throttle control signal to the engine control unit, such that the DC generator outputs a predetermined power.
Preferably, the voltage control signal and the throttle control signal are algorithmically-related. The voltage control signal and the throttle control signal may be related by a quadratic equation.
It is further preferable that the auxiliary power control system includes a vehicle control unit for outputting a power control signal to the auxiliary power unit controller.
It is also preferable that the DC/DC converter comprises a plurality of semiconductor devices. The number of semiconductor devices of the DC/DC converter is preferably four, and each semiconductor device is preferably an insulated gate bipolar transistor (IGBT).
It is further preferable that the auxiliary power unit controller outputs the voltage control signal to increase an input voltage level of the DC generator, and the throttle control signal to maintain a throttle opening at a predetermined value, when an rpm of the DC generator reaches a predetermined maximum rpm (Wmax), thereby increasing the DC generator output.
Additionally, it is preferable that the auxiliary power unit controller outputs the voltage control signal to maintain the input voltage level of the DC generator, and the throttle control signal to increase the throttle opening amount of the engine, when the rpm of the DC generator reaches a predetermined minimum rpm (Wmin), thereby increasing the rpm of the DC generator.
In yet another preferred embodiment, the present invention is a method of controlling an auxiliary power system for a hybrid electric vehicle (HEV) to change from a first operational state to a second operational state. The HEV has an engine and a DC generator. The method includes generating a first throttle control signal to increase a throttle opening of the engine, and generating a first voltage control signal to maintain an input voltage level of the DC generator.
Next, when a maximum rpm is reached, a second voltage control signal is generated to increase the input voltage level of the DC generator, and a second throttle control signal is generated to maintain the throttle opening of the engine at a first predetermined amount. When the DC generator outputs a predetermined voltage, a third throttle control signal is generated to decrease the throttle opening of the engine, and a third voltage control signal is generated to maintain the input voltage level of the DC generator.
When a minimum rpm is reached, a fourth throttle control signal is generated to increase the throttle opening of the engine to a second predetermined amount, and a fourth voltage control signal is generated to maintain the input voltage level of the DC generator. Finally, a subset of the above-outlined steps are repeated until the second operational state, comprising a predetermined rpm and a predetermined power output, is reached. The subset can be a portion or all of the aforementioned steps.